1. Field of the Invention
This invention relates to an improved method and apparatus for monitoring and reporting weather conditions in a defined region, for example, airport visibility and ceiling conditions. More particularly, it relates to a method and apparatus which provides accurate, representative, and timely condition and surveillance reports without the need for human intervention. This invention has particular application to the monitoring and reporting of airport weather, and will be explained in that context here. However it will be appreciated that the invention is generally applicable to monitoring and reporting visibility, cloud ceiling, and related weather conditions generally in a defined region.
2. Description of the Prior Art
The ability of the human eye to see objects through the atmosphere is limited by the presence of airborne particles, such as moisture, ice, sand, dust, and the like. Both reflective loss and absorptive loss can cause a reduction in visibility. Reflective losses are a function of scatter coefficients and absorptive losses are a function of extinction coefficients. There have been a number of proposals in the prior art for estimating visibility, usually in a context of airport visibility. In general, these prior art systems, including the FAA's Automated Surface Observation System (ASOS), measure the transmission of a light source through the atmosphere. This approach is generally limited to sampling only small areas and extrapolating a visibility report for a larger region on the basis of these samples.
The FAA requires accurate visual weather observation of climatic conditions affecting flight operations at thousands of airfields within the National Airspace System (NAS) Systems like the Automated Surface Observation System (ASOS) report wind, ceiling, barometric pressure, dew point, and existing temperature within overall geographic areas to FAA Flight Service stations and other users. These systems, however, often do not provide the current and accurate visibility and cloud height conditions that determine the arrival/departure envelope of a specific airport's active runway(s) especially during operationally significant weather changes. To meet this requirement within the NAS today, contract observation personnel report on airport specific visibility, ceiling, and weather condition changes.
The use of contract observers is costly, and their natural attrition requires continuous training of new observers--with associated delays in filling vacancies. ASOS data is non-representative when weather is rapidly changing, which not only poses a problem in and of itself, but also creates a need for contract observers to compensate for this non-representative condition report. Finally, the unique demands of remote airfields and their lack of timely information pose a severe problem for these locations.